1. Field of the Invention
The present invention relates generally to cellular telephone communication. More specifically, the present invention relates to maintaining cellular telephone service during cluster testing.
2. Background of the Invention
Cellular telephony enjoys widespread popularity. Its growth as a means of communication has been extraordinary. Indeed, today it is virtually impossible to go anywhere without using or seeing a cellular telephone. Such growth requires that the infrastructure supporting cellular telephony be upgraded in response to this growth. Many such upgrades directly affect mobile switching centers (MSCs), and require that an old MSC be replaced with a new MSC that has upgraded capabilities.
The MSC is a critical component of modern cellular networks. Functions performed by a typical MSC include telephone call routing and billing. There can be any number of MSCs in a particular cellular telephone network. One or more base stations is connected to each MSC in a cellular telephone network. Cellular telephones in a cellular telephone network communicate with an MSC through a base station.
When a cellular telephone is turned on or moves to an area covered by another MSC, the cellular telephone registers with the MSC whose coverage area it is in. Registration provides information to the cellular telephone system that is required for among other things, routing telephone calls to and from the cellular telephone. This information includes location information, such as the cellular telephone's identification and the point code of the MSC with which the cellular telephone registered.
The location information is stored in a home location register. During registration, the MSC sends a registration message to a home location register (HLR). The registration message contains the location information to be stored in the HLR. Consequently, after registration a query to the HLR can locate any active cellular telephones in a cellular telephone system.
In many systems, the HLR is centralized and accessible to entities that need to determine the location of a particular cellular telephone in a network. Use of a centralized HLR eliminates the need to maintain an HLR on each MSC in a cellular telephone network. In large cellular networks, this greatly reduces the cost of the system and facilitates implementation of fault tolerant features such as redundant HLRs.
When an old MSC is to be upgraded by replacement with a new MSC, the new MSC and the base stations that it will service must be tested. Testing of such cellular clusters is often referred to as “cluster” testing. When a new MSC is switched into operation in a network it is said to be “cut” into the network.
One significant problem with cutting a new MSC into a cellular network in conventional systems is that there was no new point code assigned to the new MSC. The intent was to assign the point code of the old MSC to the new MSC when the old MSC was retired. However, prior to the time when the new MSC is declared operational cellular telephones being serviced by base stations in the coverage area of the new MSC would not be able to be receive telephone calls. This is because the new MSC bad the same point code as the old MSC. Prior to the new MSC being declared operational, the old MSC is still in the system. Consequently, when the system tried to locate a cellular telephone that had registered on the new switch, it would not know whether the point code referred to the old MSC or the new MSC.
To avoid this ambiguity, the new MSC was assigned a temporary point code (TPC). The TPC is a unique point code that uniquely identifies the new MSC. Once testing is complete, and the old MSC is removed from service, the TPC is replaced with the old MSC's point code.
Unfortunately, use of the TPC created a new set of problems. One problem was the fact that prior to the time the new MSC was placed into operation, there were no land line trunks to the new MSC. Voice trunks to the new MSC could not be accommodated because the local exchange carrier (LEC) was not aware of the TPC that had been assigned to the new MSC. Rather the land line switch, for example, a local exchange carrier (LEC), was in communication with the old MSC using the old MSC's point code. Consequently, there were no voice path trunks from the LEC to the new MSC. The lack of trunks to the LEC prevented a cellular telephone that had registered on the new MSC from making a telephone call to a land line telephone, as well as preventing a land line telephone from completing a telephone call to a cellular telephone registered on the new MSC.